Biogeochemical cycles• Our planet consists of many complex, large-scale,interacting systems.• System = a network of relationships among a group ofparts, elements, or components that interact with andinfluence one another through the exchange of energy,matter, and/or informationFeedback loops: Negative feedbackFeedback loop = a circular process whereby a system’soutput serves as input to that same systemIn a negative feedback loop, output acts as input thatmoves the system in the opposite direction.This compensation stabilizes the systemFeedback loops: Positive feedback• In a positivefeedback loop,output acts asinput that movesthe systemfurther in thesame direction.• Thismagnification ofeffectsdestabilizes thesystem.Dynamic equilibrium, homeostasis• Dynamic equilibrium or steady state = when processesin a system move in opposite directions at equivalentrates so their effects balance out… this can be largeforces pulling in opposite directions yielding small to nochange• Homeostasis = tendency of a system to maintain constantor stable internal conditions• Earth’s climate and an animal’s body are examples ofhomeostatic systems in dynamic equilibrium.Dynamic equilibrium• Many equilibrium states can exist… there is rarelyjust one• Linear versus non-linear changes = movement fromone steady state to another can be gradual, or abrupt• Earth’s climate is an example of a system with manysteady states and abrupt changes (examples)Closed and open systems• Closed system = isolated and self-contained• Open system = exchanges energy, matter, andinformation with other systems• The Earth is basically a closed system with respect tomass, but open with respect to energy• But any system is open if we examine it closely enough orlong enough.System example: the Mississippi River Delta“Dead Zone”A systems approach allows us to expand or contract ourarea of interest as problems requireConnected systems• The farms of Minnesota and the Gulf of Mexico interact.• Understanding the dead zone requires viewing farms inthe Mississippi River drainage and the Gulf of Mexico asa single system.• This holistic kind of view is necessary for comprehendingmany environmental issues and processes… consider theproblems that compartmentalizing the governmentagencies causes here…EutrophicationKey to the dead zone = Eutrophication: excess nutrient enrichment in water, which increases production of organic matter...… which when decomposed by oxygen-using microbes can deplete water of oxygen.Increasing nitrogen inputsNitrate concentrationsin Midwestern rivers in1980–98 were muchmore than in 1905–07.Amount of nitrogenfertilizer used rosegreatly, 1950–80Creation of the hypoxic dead zoneNitrogen input boosts phytoplankton……which die and are decomposed by microbes that suckoxygen from water, killing fish and shrimp.Importance of systems• The problem persisted because government agencies thatregulated pesticide use did not interact with those thatregulated fisheries… systems approach is not a hallmarkof government• The problem continues to persist because of the linkagesof systems… if farming is regulated, excess nutrients stillin the soil and river sediments continue to leach out.• Systems that are hard to pollute are often hard to cleanup… we will see this in many biogeochemical cyclesEarth’s structural spheres• Lithosphere = rock, sediment, soil below Earth’s surface• Atmosphere = air surrounding the planet• Hydrosphere = all water—salt and fresh, liquid, ice, andvapor• Biosphere = all the planet’s living things, and the abioticparts of the environment with which they interactBiogeochemical cycles• Nutrients are elements and compounds that organismsconsume and require for survival.• Nutrients stimulate production by plants, and the lack ofnutrients can limit production.• Nutrients move through ecosystems in nutrient cycles orbiochemical cycles.Nutrients• Macronutrients are elements and compounds required inrelatively large amounts and include nitrogen, carbon,and phosphorous.• Micronutrients are nutrients needed in small amounts…but just as critical for survivalTerminology and Concepts• All matter cycles...it is neither created nor destroyed...• Biogeochemical cycles: the movement (or cycling) ofmatter and energy through a system• by matter we mean: elements (carbon, nitrogen, oxygen)or molecules (water)• so the movement of matter (for example carbon) betweenthese parts of the system is a biogeochemical cycleTerminology and Concepts• Reservoir: a unique, definable collection of a material ofinterest… also called a pool…• Flux: the movement of a material of interest from onereservoir to another• Residence time: the average amount of time somethingspends in a reservoir• Residence Time = Reservoir size/fluxThe importance of residence times• Reservoirs with Long residence times are hard to pollute,but once polluted, hard to clean up• Reservoirs with Short residence times are easy to pollute,but once polluted, easier to clean up… maybe…• Key is that cycles exist, so long residence times reservoirscan be connected to those with short residence times.Example: CO2 and the ocean… “CO2 is forever”…more on this laterMississippi River “dead zone” exaampleThe carbon cycleThe carbon cycleHow carbon (C) moves through our environment• Producers pull carbon dioxide (CO2) from the air and use itin photosynthesis.• Consumers eat producers and return CO2 to the air byrespiration.• Decomposition of dead organisms, plus pressureunderground, forms sedimentary rock and fossil fuels.This buried carbon is returned to the air when rocks areuplifted and eroded.• Ocean water also absorbs carbon from multiple sources,eventually storing it in sedimentary rock or providing it toaquatic plants.Key facts in the carbon cycle• How much carbon is where?• Most carbon is in rocks (carbonates and other sediments)• Most carbon not in rocks is in the ocean• There is more carbon in the atmosphere than in livingplants• About 3 times more carbon in soils than in land plants• There is 6 times more carbon in fossil fuels than in theatmosphere.• There is 8 times more carbon in fossil fuels than in livingplantsHuman impacts on the carbon cycle• We have increased CO2 in the atmosphere by burningfossil fuels and deforesting forests.• Atmospheric CO2 concentrations are the highest